Non-contacting RF-ID card for wide voltage range input

ABSTRACT

A battery-free non-contacting information card of a relatively simple arrangement which prevents an IC chip or the like from being destroyed by an excess voltage. This non-contacting information card includes a resonance circuit (3) for receiving a carrier signal (e.g., FSK signal) modulated on the basis of information supplied from a card reader/writer (2), an information processing systems (5), (6), (7) for obtaining information from the carrier signal and a rectifier systems (13) for obtaining a voltage by rectifying the carrier signal, wherein the non-contacting information card can be operated by the voltage obtained at the output side of the rectifier circuit (13). The resonance circuit (3) includes a variable capacitive element (3d). A resonance frequency of the resonance circuit (3) is varied by varying the capacity value of the variable capacitive element (3d) in response to the voltage value obtained at the output side of the rectifier circuit (13) to thereby make the voltage value obtained at the output side of the rectifier circuit (13) substantially constant.

This is a division of application Ser. No. 08/491,077 filed Jun. 16,1995, now U.S. Pat. No. 5,652,423.

BACKGROUND OF THE INVENTION

The present invention relates to a non-contacting information card foruse as commuter's tickets, management cards for animals and lift ticketsfor a skiing ground and which can transmit and receive information toand from a card reader/writer by radio waves.

Non-contacting information cards which can transmit and receiveinformation, such as identification (ID) number, due data and the numberof times, between it and a card reader/writer via radio waves haverecently been used as commuter's tickets, management cards for animalsand lift tickets for a skiing ground, for example.

While the non-contacting information cards have heretofore been operatedby a battery, in order to reduce the thickness of the non-contactinginformation card and to facilitate the management of the non-contactinginformation card, proposed non-contacting information cards are notoperated by batteries but they can be operated by a voltage whichresults from rectifying a carrier signal used to transmit informationfrom the card reader/writer.

FIG. 1 of the accompanying drawings shows an example of an informationcard system using a non-contacting information card which is notoperated by a battery. This information card system will be describedbelow with reference to FIG. 1.

As shown in FIG. 1, fundamentally, the information card system iscomposed of a non-contacting information card 1 and a card reader/writer2 for transmitting and receiving information between it and thenon-contacting information card 1 via radio waves.

As shown in FIG. 1, the card reader/writer 2 includes a main controlunit 21 consisting of a CPU (central processing unit), a signal inputterminal 22, a signal controller 23, a data buffer RAM (random-accessmemory) 24 and a high-order interface controller 25. Transmissioninformation from the main control unit 21 is supplied through a PS/SP(parallel-to-serial/serial-to-parallel) converter 26 which convertsinformation supplied thereto in the parallel to serial form to a FSK(frequency shift keying) modulator 27.

The FSK modulator 27 sets a frequency f₁ to 320 kHz, for example, when adigital signal is at high "1" level and sets a frequency f₂ to 280 kHz,for example, when the digital signal is at low "0" level. The cardreader/writer 2 shown in FIG. 1 further includes a reference oscillator28 and a frequency divider 29 which divides a reference signal suppliedthereto from the reference oscillator 28 to obtain the signals with thefrequencies f₁ and f₂.

An output signal from the FSK modulator 27 is supplied through alow-pass filter (LPF) 30 and an amplifier (AMP) 31 to a coil 32 whichforms a write head.

As shown in FIG. 1, the card reader/writer 2 further includes a coil 33that forms a read head. An ASK (amplitude shift keying) signal obtainedat the coil 33 is supplied through a band-pass filter (BPF) 34 to an ASKdemodulator 35. A demodulated signal from the ASK demodulator 35 isconverted in the form of serial-to-parallel data by the PS/SP converter26 and then supplied to the main control unit 21.

Further, a voltage from a commercially-available power source issupplied to an AC input terminal 36. The voltage from thecommercially-available power source supplied to the AC input terminal 36is supplied to a power supply unit 37. The power supply unit 37 suppliesa regulated DC voltage which is used as an operation voltage to operatethe card reader/writer 2.

The non-contacting information card 1 includes a resonance circuit 3having a resonance frequency f₀ of 300 kHz, for example, for reading outthe FSK signal supplied thereto from the coil 32 constructing the writehead. The FSK signal from the resonance circuit 3 is supplied through abandpass filter (BPF) 4 to a FSK demodulator 5. Information provided inthe form of a digital signal obtained at the output side of the FSKdemodulator 5 is supplied through a PS/SP converter 6, which convertsthe information in the form of serial-to-parallel data, to a maincontrol unit 7 formed of a CPU.

The main control unit 7 supplies a memory 8 with data, such as a readcommand signal and a memory information signal. Therefore, data iswritten in or stored data is read out from the data memory 8 under thecontrol of the main control unit 7.

The digital signal, which is the information signal read out from thedata memory 8, is supplied to the main control unit 7. The digitalsignal, which is the information signal read out from the data memory 8under the control of the main control unit 7, is converted in the formof parallel-to-serial data by the PS/SP converter 6 and then supplied toan ASK modulator 9. The non-contacting information card 1 furtherincludes an oscillator 10 which supplies a carrier signal having afrequency f₃ e.g., 300 kHz to the ASK modulator 9.

An ASK signal of the information signal obtained at the output side ofthe ASK modulator 9 after the information signal has been read out fromthe data memory 8 is supplied through an amplifier (AMP) 11 to a coil 12which transmits the ASK signal to the coil 33 constructing the read headof the card reader/writer 2 in an electromagnetic coupling way.

In the example shown in FIG. 1, the FSK signal received by the resonancecircuit 3 is supplied to a rectifier 13 and a DC voltage obtained at theoutput side of the rectifier 13 is used as an operation voltage tooperate the non-contacting information card 1.

According to the non-contacting information card 1, since thenon-contacting information card is not provided with the battery, it canbe reduced in thickness and becomes useful from an administrationstandpoint.

A power for driving the non-contacting information card 1 is transmittedfrom the card reader/writer 2 in the form of electromagnetic wave.Therefore, if a positional relationship between the resonance circuit 3and the coil 32 which constructs the write head of the cardreader/writer 2 is always constant, then a voltage induced in theresonance circuit 3 becomes always constant.

However, in actual practice, when the non-contacting information card 1is in use, the non-contacting information card 1 can be moved in apredetermined area that is provided as an operation area in which thenon-contacting information card 1 can come near or away from the coil 32constructing the write head of the card reader/writer 2. Thenon-contacting information card 1 can be located randomly within thisoperation area. Therefore, when the non-contacting information card 1 islocated nearest the coil 32 of the card reader/writer 2, an excessvoltage is induced in the resonance circuit 3 of the non-contactinginformation card 1 so that the rectifier 13 outputs an excess voltage.Thus, in worst cases, there is then the risk that an IC (integratedcircuit) chip or the like disposed in the non-contacting informationcard 1 will be destroyed by the excess voltage.

In order to prevent the IC chip or the like from being destroyed by theexcess voltage, it is proposed that the non-contacting information card1 incorporates a constant voltage controller of a serial control type inassociation with the rectifier 13 to dissipate an excess voltage as aheat when the output voltage of the rectifier 13 increases in excess ofa predetermined value.

However, in this case, the constant voltage controller which treats theexcess voltage as a heat is considerably complicated in circuitarrangement and also occupies a relatively large area of the IC chip ofthe non-contacting information card 1. As a consequence, thenon-contacting information card becomes expensive.

SUMMARY OF THE INVENTION

In view of the aforesaid aspect, it is an object of the presentinvention to provide a non-contacting information card of a relativelysimple arrangement in which an IC chip or the like can be prevented frombeing destroyed by an excess voltage.

It is another object of the present invention to provide anon-contacting information card which can be made inexpensive.

According to an aspect of the present invention, there is provided anon-contacting information card including a resonance circuit forreceiving a carrier signal modulated on the basis of informationsupplied thereto from a card reader/writer, information processing meansfor obtaining information from the carrier signal and a rectifier meansfor rectifying the carrier signal to provide a voltage, thenon-contacting information card being operated by the voltage obtainedat the output side of the rectifier means. This non-contactinginformation card is comprised of a variable capacitive element providedin the resonance circuit, wherein a resonance frequency of the resonancecircuit is varied by varying a capacitive value of the variablecapacitive element in response to a voltage value of the output side ofthe rectifier means thereby to make the voltage value of the output sideof the rectifier means substantially constant.

According to another aspect of the present invention, in thenon-contacting information card, the variable capacitive element isformed of a vari-cap diode and the vari-cap diode is reversely biased bya voltage obtained at the output side of the rectifier means.

According to the present invention, the voltage obtained in theresonance circuit by the electromagnetic coupling increases so that,when the power supply voltage obtained at the output side of therectifier means increases, the capacity value of the variable capacitiveelement changes, e.g., decreases and the resonance frequency of theresonance circuit changes, e.g., increases. Therefore, the voltage thatis obtained in the resonance circuit by the electromagnetic couplingdecreases, making it possible to make the power supply voltage obtainedat the output side of the rectifier means substantially constant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing an information card systemwhich uses a non-contacting information card;

FIG. 2 is a schematic block diagram showing a non-contacting informationcard according to an embodiment of the present invention; and

FIG. 3 is a characteristic graph of frequency versus amplitude responseand to which references will be made in explaining an operation of thenon-contacting information card shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A non-contacting information card according to an embodiment of thepresent invention will hereinafter be described with reference to FIGS.2 and 3. In FIG. 2, like parts corresponding to those of FIG. 1 aremarked with the same references and therefore need not be described indetail.

As shown in FIG. 2, there is provided the resonance circuit 3 whichreceives in an electromagnetic coupling fashion the FSK signal from thecoil 32 constructing the write head of the card reader/writer 2 shown inFIG. 1.

As shown in FIG. 2, the resonance circuit 3 is composed of a coil 3a, acapacitor 3b connected in parallel to the coil 3a and a series circuitof a capacitor 3c and a vari-cap diode 3d which constructs a variablecapacitive element connected in parallel to the coil 3a.

In this case, the cathode of the vari-cap diode 3d is connected to thecapacitor 3c side and a voltage proportional to a power supply voltage,which will be described later on, is supplied to the cathode of thevari-cap diode 3d as a reverse bias voltage.

When the power supply voltage is held at a predetermined value, theresonance frequency f₀ of the resonance circuit 3 is selected to be suchone that the FSK signal from the coil 32 of the card reader/writer 2 ismade maximum by the electromagnetic coupling, e.g., 300 kHz.

In this embodiment, the FSK signal obtained in the resonance circuit 3is supplied through the bandpass filter 4 to the FSK demodulator 5. Aninformation signal based on the digital signal obtained at the outputside of the FSK demodulator 5 is converted in the form ofserial-to-parallel data by the PS/SP converter 6 and then supplied tothe main control unit 7 formed of the CPU.

The main control unit 7 supplies the data memory 8 with the signals,such as the memory information signal and the read command signal.Therefore, data is written in or read out from the data memory 8 underthe control of the main control unit 7.

The digital signal, which is the information signal read out from thedata memory 8, is supplied to the main control unit 7. The digitalsignal, which is the information signal read out from the data memory 8under the control of the main control unit 7, is converted in the formof parallel-to-serial data by the PS/SP converter 6 and then fed to theASK modulator 9. The ASK modulator 9 is supplied with the carrier signalhaving the frequency f₀, e.g., 300 kHz from the oscillator 10.

The ASK signal obtained at the output side of the ASK modulator 9 afterthe information signal has been read out from the data memory 8 issupplied through the amplifier 11 to the coil 12 which transmits the ASKsignal to the coil 33 of the read head of the card reader/writer 2 shownin FIG. 1 in an electromagnetic coupling fashion.

According to this embodiment, the FSK signal obtained in the resonancecircuit 3 is supplied to the rectifier 13 composed of a rectifier diode13a and a capacitor 13b. Then, the rectifier 13 generates a DC voltageat the output side thereof as a power supply voltage. This DC voltage isused as an operation voltage to operate the non-contacting informationcard.

According to this embodiment, a series circuit of resistors 14a and 14bis connected to two ends of the output side of the rectifier 13. Ajunction 40 between the resistors 14a and 14b is connected through ahigh frequency blocking coil 15 to a junction 50 between the capacitor3c and the vari-cap diode 3d constructing the resonance circuit 3.

Further, according to this embodiment, the non-contacting informationcard transmits and receives in an electromagnetic coupling fashioninformation between it and a card reader/writer which is similar to thecard reader/writer 2 shown in FIG. 1.

Since the non-contacting information card according to this embodimentis arranged as described above, when the non-contacting information card1 is located at the predetermined position of the operation area of thecard reader/writer 2, the rectifier 13 generates a predetermined voltageat its output side. Also, the resonance frequency of the resonancecircuit 3 is selected to be the frequency f₀ which is determineddepending on the capacity value of the initial value of the vari-capdiode 3d . Thus, the electric power is given and received between thenon-contacting information card 1 and the card reader/writer 2 at theresonance frequency f₀.

If the position of the non-contacting information card 1 is too close tothe coil 32 of the card reader/writer 2, then the voltage obtained atthe output side Of the rectifier 13 increases. However, the vari-capdiode 3d is reversely biased by a voltage corresponding to the increasedvoltage so that the capacity value of the vari-cap diode 3d decreases incorrespondence therewith. As a consequence, the resonance frequency ofthe resonance circuit 3 increases in the direction shown by adotted-line characteristic (resonance frequency f₀ +Δf) from asolid-line characteristic (resonance frequency f₀) shown in FIG. 3 toshift the resonance characteristic. Therefore, an electromagneticcoupling characteristic of the resonance circuit 3 becomesunsatisfactory and the output voltage of the resonance circuit 3 islowered. Consequently, the DC voltage obtained at the output side of therectifier 13 can be made substantially constant regardless of theposition between the coil 32 of the card reader/writer 2 and thenon-contacting information card 1.

Therefore, according to this embodiment, it is possible to prevent theIC chip or the like disposed in the non-contacting information card frombeing destroyed by the excess voltage.

While the information signal is transmitted and received between thecard reader/writer 2 and the non-contacting information card 1 in aconventional manner, according to this embodiment, the output signal ofthe resonance circuit 3 is constantly held at a substantially constantlevel. Therefore, according to this non-contacting information card, theinformation signal can be received satisfactorily and the signalprocessing can be carried out satisfactorily.

According to the present invention, the non-contacting information cardhas a relatively simple arrangement in which the resonance circuit 3includes a variable capacitive element to prevent the IC chip or thelike disposed within the non-contacting information card from beingdestroyed by the excess voltage.

Furthermore, according to the present invention, since thenon-contacting information card is relatively simple in arrangement anddoes not need a large protecting element, the inventive non-contactinginformation card can be made inexpensive.

Having described a preferred embodiment of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to that precise embodiment and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

What is claimed is:
 1. An improved non-contacting information cardincluding a resonance circuit for receiving a carrier signal modulatedon the basis of information supplied from a card reader/writer,information processing means for obtaining information from said carriersignal, and rectifier means for rectifying said carrier signal toprovide a voltage, said non-contacting information card being operatedby said voltage obtained at an output side of said rectifier means, theimprovement comprising:a first fixed capacitor; a variable capacitiveelement in series with said first fixed capacitor connected in saidresonance circuit; a high frequency blocking coil, and voltage feedbackmeans connected to said output side of said rectifier means and to aconnection between said first fixed capacitor and said variablecapacitive element via said high frequency blocking coil, wherein aresonance frequency of said resonance circuit is controlled by varying acapacity value of said variable capacitive element in response to saidvoltage at the output side of said rectifier means, and said variablecapacitive element is formed of a vari-cap diode reversely biased by aconnection to said voltage at the output side of said rectifier means,thereby preventing destruction of said non-contacting information cardby excess voltage by making said voltage at the output side of saidrectifier means substantially constant.
 2. The improved non-contactinginformation card according to claim 1, wherein said voltage feedbackmeans include first and second fixed resistors connected in seriesbetween said output side of said rectifier means and ground, therebyoperating as a voltage divider.
 3. The improved non-contactinginformation card according to claim 2, wherein said rectifier meansinclude:a diode; a second fixed capacitor connected to an output side ofsaid diode and to ground.
 4. The improved non-contacting informationcard according to claim 3, wherein said information processing meansinclude:a bandpass filter; a demodulator connected to said bandpassfilter; a control unit to process an output of said demodulator; and amodulator to modulate for transmission an output of said control unit.